The present invention relates generally to apparatus for processing of a semiconductor wafer, and more particularly to a cold trapping system with a visual indicator to allow monitoring the adequacy of the cold trap.
Semiconductor processes use vapor precursors for processing of thin films on an integrated circuit (IC) substrate. The majority of these vapor precursors, together with their by-products are pumping out and exhausted to a waste stream.
It is very expensive to collect and dispose of the precursor exhaust products. Further, these non-reactive precursors and these byproducts can be hazardous and harmful to the environment. The IC industry is forced to conform to ever more stringent regulations concerning the storage and disposal of these wastes.
It is very inconvenient to collect waste as a gas because it is difficult to transport and bulky to store. It is more convenient if the waste can be converted, at least partially into a solid or liquid waste. It is well known to use cold traps to completely condense some chemical vapors. It is also well known to use cold traps to condense elements of a precursor to at least simplify the waste collection process.
In a chemical vapor deposition (CVD) process, high temperature process is often used. Because of the low efficiency of the CVD process, a hot trap is recommended for completing the CVD reaction, leaving only the by-products to the exhaust stream. An example is copper CVD process. Copper CVD process uses copper-hfac-tmvs precursor to deposit copper on a hot surface (xcx9c200xc2x0 C.) following the reaction:
2 Cu-hfac-tmvsxe2x86x92Cu+Cu(hfac)2+2 tmvs (at  greater than xcx9c100xc2x0 C.)
The reaction occurs at temperature higher than xcx9c100xc2x0 C. The efficiency of this reaction is roughly 10-20%, thus 80-90% of the precursor leaves the process chamber un-reacted. A cold trap would then collect the precursor Cu-hfac-tmvs, and the by-products Cu(hfac)2 and tmvs. Using a hot trap before the cold trap, most of the precursor would further reacts, leaving only the by-products in the waste stream.
FIG. 1 shows a prior art apparatus for a cold trap. The precursor exhaust enters the cold trap at the cold trap input 23, converting some elements of the exhaust into non-gaseous phase at the waste collection surface 15, and exhaust the gaseous phase to the cold trap output 25. The cooler means 37 serves to cool the waste collection surface 15 to a trapping temperature where the precursor exhaust reacts and separates into non-gaseous and gaseous components. The non-gaseous components trapping at the waste collection surface 15 could travel to the waste drain collection 45. The waste collection 45 has a drain valve 43 to keep the waste stored.
The major disadvantage of this prior art is the inability to quickly evaluate the adequacy of the cold trap. If the cold trap is not efficient enough, material can travel downstream of the cold trap and might deposit outside of the cold trap. If there is some problem upstream of the cold trap, such as a cold section of the pipe leading to the cold trap, material can deposit outside of the cold trap.
A co-application titled xe2x80x9cHigh pressure chemical vapor trapping systemxe2x80x9d of the same author, Tue Nguyen, provides a high pressure trapping system composing of a hot trap for completing the reaction and a cold trap for trapping the residue.
FIG. 2 shows the high pressure chemical vapor trapping system. The exhaust from the processing chamber 110 is pumped away by the vacuum pump 130. The pressure in the process chamber foreline 115 is normally low, in the range of torr or millitorr pressure. After the vacuum pump, the pressure is almost atmospheric at the vacuum pump exhaust 135. The hot trap 120 converts un-reacted precursors to the precursor by-products, and the cold trap 140 converts the gas phase by-products to non-gaseous phase by-products for easily transport and storage. This system connects to the downstream of the vacuum pump to take advantage of the high pressure at the pump exhaust. By not disturbing the chamber configuration, there is no potential contamination of the process. Using this system, there is no observable degradation to the vacuum pump, and no contamination to the process chamber.
There is no visual indicator to show whether or not the hot trap is converting all reaction elements, and there is no visual indicator that the cold trap is trapping all waste elements.
It would be advantageous if there is a visual indicator allowing the monitoring of the adequacy of the cold trap.
Accordingly, a visual indicator cold trapping system to allow monitoring the adequacy of the cold trap is provided. The system comprises a cold trap having an input port, a output port, a waste collection surface, a cooler means to cool the trap to a temperature in the range from 25 degrees to minus 200 degrees Celsius. The cold trap provides non-gaseous wastes at the waste collection surface, and gaseous exhaust at the gas output port. For visual indicator, the cold trapping system comprises a plurality of hollow transparent connectors.
In some aspects of the invention, the hollow transparent connector is connected to the input of the cold trap. Its transparency property allows the visual inspection of the cold trap for any material deposited there. Any material deposited in this transparent connector implies that there is problem upstream of the cold trap. Since there is material deposited in the connector section, it is likely that there is also material deposited in the pipe upstream of the cold trap. The visual indicator allows the problem to be spotted immediately and to alert the operator to take appropriate actions. In some aspects of the invention, the transparent connector has a heater means to bring its temperature to be the same as the upstream pipe. This allows the connector to be at the same temperature as the upstream pipe, thus eliminates the possibility of material deposition due to temperature difference. In some aspects of the invention, the input of the cold trap has a transparent section, served as the connector itself.
In some aspects of the invention, the hollow transparent connector is connected to the output of the cold trap. Any material deposited in this transparent connector implies that there is problem downstream of the cold trap. Since there is material deposited in the connector section, there is likely that there is material exhausted from the cold trap without being trapped there. In some aspects of the invention, the transparent connector has a heater means to bring its temperature to be the same as the downstream pipe. This allows the connector to be at the same temperature as the downstream pipe, thus eliminates the possibility of material deposition due to temperature difference.
In some aspects of the invention, the visual indicator cold trapping system further comprises a waste drain with a hollow transparent connector. In some aspects of the invention, the drain section is transparent to allow visual inspection of the collected material.
In other aspects of the invention, a high pressure chemical vapor trapping system to separate and collect elements of a chemical vapor exhaust with a visual indicator cold trap is provided. The system comprises a hot trap and a visual indicator cold trap connected to each other as a single unit. The exhaust pump is upstream of the trapping system, providing a high pressure in the hot trap.
The present invention system comprises a hot trap having an input port, a gas output port, a waste collection surface, and a heater. The heater heats the hot trap to a temperature in the range from 100 to 500 degrees Celsius. The hot trap accepts chemical vapor such as the above-described copper precursors and provides non-gaseous wastes at the waste collection surface, and gaseous exhaust at the gas output port at a pressure substantially the same as the input pressure.
The system also comprises a visual indicator cold trap having an input port operatively connected to the gas output port of the hot trap, a gas output port, a waste collection surface, and a plurality of hollow transparent connectors operatively connected to the ports of the cold trap. The cold trap cools the chamber to a temperature in the range from 25 degrees to minus 200 degrees Celsius. The cold trap provides non-gaseous wastes at the waste collection surface, and gaseous exhaust at the gas output port at a pressure substantially the same as the input pressure. In this manner, vapor byproducts are collected in two stages. The visual indicator allows the determination of the adequacy of the trapping system. If the hot trap is not adequate, meaning allowing waste elements to escape the hot trap, the waste elements will show up at the visual indicator at the input of the cold trap. If the cold trap is not adequate, meaning allowing waste elements to escape the cold trap, the waste elements will show up at the visual indicator at the output of the cold trap. In some aspects of the invention, the cold trap further comprises a drain section for waste storage. The drain section also comprises a visual indicator for visual inspection.
The invention also provides that an exhaust pump, operatively connected to hot trap input port, provides gaseous exhaust to the hot trap. In this manner, a high pressure is created at the hot trap gas input port.
In some aspects of the invention, the chemical vapor exhaust is a MOCVD precursor such as Cu(hfac) combined with a ligand (Cu(hfac)L). Then, the first chamber includes a plurality of metal plates, or other heated structures extending into the hot trap. These metal plates are of the same metal as in the MOCVD precursor and act as metal collection surfaces. That is, the collection surface acts as the heater in the hot trap. As the precursor vapor is heated, metal from the precursor is deposited on the metal plates as the heat completes the chemical reaction. The metal collection surface/heaters are reclaimed from recycling when a predetermined amount of solid metal waste is collected on the collection surfaces.
In some aspects of the invention, the both the hot and cold chambers are easily removable for efficient recycling of the collected waste materials. A first exhaust line extends to the exhaust input port of the hot trap. The first line including at least one valve to block the passage of gas from the deposition chamber. Likewise, a second exhaust line extends from the hot trap gaseous exhaust port, and also includes at least one valve to block the escape of gas from the second line.
The hot trap includes a first valve at the exhaust input port and a second valve at the gaseous exhaust port. The hot trap is removable from the first and second lines for waste removal, when full. In this manner, the first and second valves in said hot trap prevent exhaust from escaping from the trap, when the trap is disconnected. The valves in the first and second lines prevent the escape of exhaust from the system when the hot trap is removed. In the same manner, valves are used in the gas lines going to and from the cold trap, and also used in the input and output gas ports. Then, the cold trap is also easily removable without allowing the escape of vapors from the system.
Sometimes the hot trap collection surfaces are biased with a voltage, whereby charged metal from the MOCVD precursor is attracted and deposited on said collection surface. In other aspects of the invention, the hot trap includes a second input port to accept a catalyst selected from the group consisting of water, alcohol, and ammonia, whereby the catalyst furthers the chemical reaction in the first chamber.